Resonance spectrum taken with an electrostatic drive. Plot of the amplitude versus frequency of the (a) fundamental mode at 10 MHz and (b) the higher mode at 35 MHz with increasing while remains fixed. Inset: plot of the resonant peak amplitude with increasing . Dependence of the (c) amplitude and (d) frequency as function of at fixed where the solid squares and triangles represent the fundamental and higher mode respectively [124].
